Japanese Laid-open Patent Publication No. 2010-077960 discloses a technique for controlling an electronic throttle valve by selecting, when a driver demand drive force (i.e., a drive force demanded by the driver and calculated based on an accelerator opening degree) is greater than a target drive force for limiting vehicle speed, the smaller of these two, that is to say, the target drive force for limiting vehicle speed, so that actual vehicle speed does not exceed a limit vehicle speed.
Here, a configuration is assumed in which an acceleration for limiting vehicle speed (referred to as “vehicle speed limit acceleration”, hereinafter) is calculated based on a difference between actual vehicle speed and limit vehicle speed, a target drive force for limiting vehicle speed (referred to as “vehicle speed limit drive force”, hereinafter) is calculated based on the vehicle speed limit acceleration, a driver demand drive force is calculated based on an accelerator opening degree, and a drive force is controlled based on the smaller of the vehicle speed limit drive force and the driver demand drive force. In other words, when the driver demand drive force is greater than the vehicle speed limit drive force, the drive force is limited to the vehicle speed limit drive force.
Here, a state in which the vehicle speed limit drive force is smaller than the driver demand drive force and thus the drive force is controlled based on the vehicle speed limit drive force is referred to as “a limit state”, and a state in which the vehicle speed limit drive force is greater than the driver demand drive force and thus the drive force is controlled based on the driver demand drive force is referred to as “a non-limit state”. The vehicle speed limit drive force is calculated based on the vehicle speed limit acceleration; however, in order to reduce a probability that the actual vehicle speed exceeds the limit vehicle speed, it is necessary to correct the vehicle speed limit drive force based on a traveling circumstance. Because the drive force is controlled based on the vehicle speed limit drive force in the limit state, the vehicle speed limit drive force can be corrected based on an accumulated value obtained by accumulating a difference between an actual acceleration and the vehicle speed limit acceleration in cycles. However, constantly performing such a correction in the limit state leads to the following problem. For example, at an uphill road, there is a case where the vehicle speed limit drive force becomes greater than a maximum drive force that can be generated by a drive force generation apparatus. In such a case, the actual acceleration does not follow the vehicle speed limit acceleration, which causes the difference between the actual acceleration and the limit acceleration to become greater. The accumulation of such a difference in cycles causes the vehicle speed limit drive force to be corrected excessively. After a transition from the uphill road to a flat road, the vehicle speed limit drive force, which has been corrected excessively during the traveling on the uphill road, does not work, which may cause the actual vehicle speed to exceed the limit vehicle speed.
Therefore, it is an object of one aspect of the disclosure to provide a vehicle speed limit apparatus that can reduce a probability of an actual vehicle speed exceeding a limit vehicle speed after a transition from an uphill road to a flat road.